set.seed(0)
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                      cache=TRUE,cache.extra = knitr::rand_seed,
                      dpi = 300, fig.width = 13.3, fig.height = 10)
#library(viridis)
library(tidyverse)

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library(scales)

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library(lubridate)

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options(scipen = 999)
library(latex2exp)


MIN_VALID_YEAR <- 6

variable_of_interest<- "Bt/K Lutjanus malabaricus"
x_labeller<- scales::percent

## [1] 594

## [1] 174

Intro

###Simplified model:

2 species (Lutjanus malabaricus + Pristipomoides multidens)
10x10 simple map
2 populations (0-9; 10+)

Things we don’t know:

Initial population
Carrying capacity
Current depletion and the like

Things we know:

Last year landings
SPR
data we collected

Approach:

Start the fishery “ab novo”
Repeatedly:
- Randomize all parameters \(K,L_{\inf},\dots\)
- Run simplified POSEIDON for “many” years (up to 40)
  - Free entry
- Accept simulation if landings/spr are the same as what we observe in data
Collect

Benefits: * No need for population reconstruction * Clear uncertainty propagation * Clear value of information Cost: * Model needs to be fast

Results * Ran the model for about 50,000 times * Accepted about 0.5% of them * This is their story….

Weighing evidence

Imagine we only knew what this year landings (no length data)
- 5000t to 10000t for malabaricus
- 1000t to 3000t for multidens

## [1] 266

How does it change if I also add as a condition
- OBSERVED SPR of malabaricus must be between 0.2% and 20% (measures from 2018 and 2016 but adding a bit of pessimism) respectively

How does knowing that the SPR of the other species is between 10 and 20 help?

First basic result:

Once SPR is properly contextualized within the history of the fishery; these are actually green shoots
Measuring the SPR of another species can increase our expected estimate of depletion for this species

ADD MORE:

I know that both boat populations are still at it
I know that small boats are more numerous
I know that malabaricus SPR has dropped dramatically?

Policy

We don’t want just to assess, we want to know policy effects:

no policy
put a 100 day limit to 10GT only
put a 100 day limit to all

Works as before but: * apply same policy to all accepted runs

Positive: * study the average effect * understanding the uncertainty Negative: * to make them comparable, speak only in relative terms

Depletion policy

limited_poseidon_demo

Ernesto Carrella

1/16/2020

Intro

Weighing evidence

Policy